Income Taxes - Tax loss, tax credit and interest carryforwards (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Operating Loss Carryforwards [Line Items]
Total tax loss, tax credit and interest carryforwards	$ 256.4	$ 259.2
Expires within 10 years
Operating Loss Carryforwards [Line Items]
Tax loss carryforwards (tax effected)	23.0	78.7
Tax credit carryforwards	0.6	1.6
Interest carryforwards	2.0	2.9
Expires after 10 years or indefinite
Operating Loss Carryforwards [Line Items]
Tax loss carryforwards (tax effected)	172.1	115.8
Tax credit carryforwards	9.2	17.3
Interest carryforwards	$ 49.5	$ 42.9